1. Field of the Invention
The present invention relates to a liquid crystal display device for displaying marks such as characters and symbols with the use of liquid crystal.
2. Description of the Related Art
In order to realize bright display, there is employed a display system which does not use a polarizing plate, specifically, a display device which uses polymer dispersed liquid crystal or guest-host liquid crystal in which a dye (guest) and liquid crystal (host) are mixed. The polymer dispersed liquid crystal includes microencapsulated liquid crystal in which liquid crystal is confined in a polymer resin in advance, polymer network liquid crystal, and the like. A polymer network liquid crystal panel (hereinafter, referred to as PN liquid crystal panel) which uses the polymer network liquid crystal (hereinafter, referred to as PN liquid crystal) can perform low voltage driving. The PN liquid crystal is a composite liquid crystal material in which a polymer resin which polymerizes under ultraviolet light and general TN liquid crystal are mixed. When this liquid crystal material is irradiated with ultraviolet light, the polymer forms a network, and at the same time, the TN liquid crystal is uniformly dispersed in the polymer network. As a result, functions of both of the polymer and the TN liquid crystal may be simultaneously achieved.
The PN liquid crystal panel is a light-scattering liquid crystal display element, which scatters incident light with the use of a difference in refractive index between the polymer network and the TN liquid crystal. Therefore, a polarizing plate and an alignment film are unnecessary, which have been used in a conventional TN liquid crystal device. Therefore, light loss is extremely small, and bright display is possible.
However, the PN liquid crystal has bad steepness, which makes it difficult to perform multi-division driving, and hence static driving is mainly employed. Therefore, when a complex shape is to be displayed, there arises a problem that the number of wirings increases, and hence the display of those wirings becomes adversely visible. In order to solve the problem, transparent conductive films are laminated, and the wiring is formed of a transparent conductive film in the lower layer, to thereby make the display of the wiring invisible.
FIG. 12 is a cross-sectional view of a PN liquid crystal panel in which PN liquid crystal is injected between two transparent substrates. On a surface of a first substrate 61 on the lower side, a first transparent electrode 63 and an insulating layer 64 are formed. On the insulating layer 64, a second transparent electrode 58 and a peripheral electrode 60 are separately formed. The first transparent electrode 63 and the second transparent electrode 58 are connected to each other via a contact hole 57 opened in the insulating layer 64. On an entire surface of a second substrate 62, a third transparent electrode 59 is formed. The first substrate 61 and the second substrate 62 are adhered to each other by a sealing material 51, and PN liquid crystal 79 is injected between both the substrates (for example, see JP 2001-125086 A).
The PN liquid crystal is in a light scattering state when no electric field is applied, and is in a transmitting state when an electric field is applied. When a voltage is applied between the first transparent electrode 63 and the third transparent electrode 59, an electric field is applied to the PN liquid crystal 79 between the second transparent electrode 58 and the third transparent electrode 59, and thus the PN liquid crystal 79 transmits light. When the peripheral electrode 60 formed in the periphery of the second transparent electrode 58 is set to the same potential as the third transparent electrode 59, the PN liquid crystal 79 between the peripheral electrode 60 and the third transparent electrode 59 maintains the light scattering state. When the first transparent electrode 63 and the third transparent electrode 59 are set to the same potential, the PN liquid crystal 79 enters the light scattering state. Further, when the peripheral electrode 60 and the second transparent electrode 58 are set to the same potential, the PN liquid crystal 79 between the peripheral electrode 60 and the third transparent electrode 59 enters the light transmitting state. When the first transparent electrode 63 formed under the insulating layer 64 is used as the wiring, it is possible to intersect the second transparent electrode for forming an image with the wiring. In other words, a complex pattern for forming an image can be formed.
FIG. 13 is a cross-sectional view of a PN liquid crystal panel. PN liquid crystal 79 is injected in a clearance between two glass substrates 71 and 72. A display electrode 73a and a wiring electrode 73b are formed on the glass substrate 71. An insulating layer 74 and an outer electrode 75 are laminated on outer portion of the display electrode 73a. Also on the wiring electrode 73b, the insulating layer 74 and the outer electrode 75 are laminated. Also on the surface of the counter substrate 72, a display electrode 76a, a wiring electrode 76b, an insulating layer 77, and an outer electrode 78 are similarly formed. The counter substrate 72 is disposed so as to be opposed to the glass substrate 71. Display is performed by applying an electric field between the display electrodes 73a and 76a (for example, see JP 2007-133088 A). The wiring electrodes 73b and 76b are electrically blocked by the outer electrodes 75 and 78, respectively, and hence the regions corresponding to the wiring electrodes 73b and 76b are not displayed. That is, display is performed in a region 70B, and regions 70A become non-display regions. Further, no gap is formed between the outer electrode 75 (78) and the display electrode 73a (76a), and hence a boundary therebetween is invisible.
FIG. 14 illustrate a plane structure of a liquid crystal panel capable of simultaneously displaying isolated electrodes, which are surrounded by closed display electrodes, and an outer electrode (for example, see JP 2008-9386 A). On a substrate, a first transparent conductive layer, an insulating layer, and a second transparent conductive layer are laminated in the stated order. FIG. 14(a) is a plan view illustrating the second transparent conductive layer, FIG. 14(b) is a plan view illustrating the insulating layer, and FIG. 14(c) is a plan view illustrating the first transparent conductive layer. As illustrated in FIG. 14(c), on a glass substrate 910, wiring electrodes 911 and an outer electrode terminal 912 are formed of the first transparent conductive film. On the first transparent conductive film, as illustrated in FIG. 14(b), an insulating layer 930 in which through holes H1 to H4 are formed is provided. On the insulating layer, as illustrated in FIG. 14(a), mark electrodes 931, isolated electrodes 932, and an outer electrode 933 are formed of the second transparent conductive layer. The wiring electrode 911 and the mark electrode 931 are electrically connected to each other via the through hole H1, the isolated electrode 932 and the outer electrode 933 are electrically connected to each other via the through holes H2 and H4, and the outer electrode 933 and the outer electrode terminal 912 are electrically connected to each other via the through hole H3. With this structure, the isolated electrode 932 is set to the same potential as the outer electrode 933, and hence the isolated electrode 932 and the outer electrode 933 may perform the same display.
In the PN liquid crystal panel illustrated in FIG. 12, a gap is present between the second transparent electrode 58 and the peripheral electrode 60, and the PN liquid crystal in the gap region is in the light scattering state. Further, a part of the first transparent electrode 63 as the wiring electrode intersects with the gap region through intermediation of the insulating layer 64. Therefore, when a voltage is applied to the first transparent electrode 63 in order to cause the PN liquid crystal 79 on the second transparent electrode 58 to enter the light transmitting state, a voltage dropped due to the insulating layer 64 is applied to the surface of the insulating layer 64 at the gap of the intersecting portion. As a result, there occurs a trouble that a part of the gap region is half-lit. In order to prevent this phenomenon, it is effective to form the insulating layer 64 thick, but in this case, the manufacturing cost increases because, for example, a long time period is required to form the insulating layer 64, and also a long time period is required to form the contact hole 57.
In the PN liquid crystal panel illustrated in FIG. 13, the outer electrodes 75 and 78 and the display electrodes 73a and 76a are formed without a gap therebetween in a direction normal to the surface of the substrate. However, in actuality, it is extremely difficult to form the electrodes without a gap therebetween. In order to bring leading edge portions of the display electrodes 73a and 76a and leading edge portions of the outer electrodes 75 and 78 into a line, high accuracy mask alignment and high accuracy etching technology are necessary. As a result, an expensive manufacturing device is necessary, and it becomes impossible to avoid the cost increase.
In the liquid crystal panel illustrated in FIG. 14, the mark electrodes 931, the isolated electrodes 932, and the outer electrode 933 are formed of the second transparent conductive layer, and hence a clearance is generated between the mark electrode 931 and the isolated electrode 932, and similarly a clearance is generated between the mark electrode 931 and the outer electrode 933. The PN liquid crystal in those gaps is in the light scattering state, and the clearances become visible when the periphery thereof is in the light transmitting state, which degrades the display quality.